/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.eclipse.leshan.core.util;

import java.util.Random;

/**
 * <p>
 * Operations for random <code>String</code>s.
 * </p>
 * <p>
 * Currently <em>private high surrogate</em> characters are ignored. These are unicode characters that fall between the
 * values 56192 (db80) and 56319 (dbff) as we don't know how to handle them. High and low surrogates are correctly dealt
 * with - that is if a high surrogate is randomly chosen, 55296 (d800) to 56191 (db7f) then it is followed by a low
 * surrogate. If a low surrogate is chosen, 56320 (dc00) to 57343 (dfff) then it is placed after a randomly chosen high
 * surrogate.
 * </p>
 *
 * <p>
 * #ThreadSafe#
 * </p>
 *
 * @author Apache Software Foundation
 * @author <a href="mailto:steven@caswell.name">Steven Caswell</a>
 * @author Gary Gregory
 * @author Phil Steitz
 * @since 1.0
 * @version $Id: RandomStringUtils.java 1056988 2011-01-09 17:58:53Z niallp $
 */
public class RandomStringUtils {

    /**
     * <p>
     * Random object used by random method. This has to be not local to the random method so as to not return the same
     * value in the same millisecond.
     * </p>
     */
    private static final Random RANDOM = new Random();

    /**
     * <p>
     * <code>RandomStringUtils</code> instances should NOT be constructed in standard programming. Instead, the class
     * should be used as <code>RandomStringUtils.random(5);</code>.
     * </p>
     *
     * <p>
     * This constructor is public to permit tools that require a JavaBean instance to operate.
     * </p>
     */
    public RandomStringUtils() {
        super();
    }

    // Random
    // -----------------------------------------------------------------------
    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of all characters.
     * </p>
     *
     * @param count the length of random string to create
     * @return the random string
     */
    public static String random(int count) {
        return random(count, false, false);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of characters whose ASCII value is between <code>32</code> and
     * <code>126</code> (inclusive).
     * </p>
     *
     * @param count the length of random string to create
     * @return the random string
     */
    public static String randomAscii(int count) {
        return random(count, 32, 127, false, false);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of alphabetic characters.
     * </p>
     *
     * @param count the length of random string to create
     * @return the random string
     */
    public static String randomAlphabetic(int count) {
        return random(count, true, false);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of alpha-numeric characters.
     * </p>
     *
     * @param count the length of random string to create
     * @return the random string
     */
    public static String randomAlphanumeric(int count) {
        return random(count, true, true);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of numeric characters.
     * </p>
     *
     * @param count the length of random string to create
     * @return the random string
     */
    public static String randomNumeric(int count) {
        return random(count, false, true);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of alpha-numeric characters as indicated by the arguments.
     * </p>
     *
     * @param count the length of random string to create
     * @param letters if <code>true</code>, generated string will include alphabetic characters
     * @param numbers if <code>true</code>, generated string will include numeric characters
     * @return the random string
     */
    public static String random(int count, boolean letters, boolean numbers) {
        return random(count, 0, 0, letters, numbers);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of alpha-numeric characters as indicated by the arguments.
     * </p>
     *
     * @param count the length of random string to create
     * @param start the position in set of chars to start at
     * @param end the position in set of chars to end before
     * @param letters if <code>true</code>, generated string will include alphabetic characters
     * @param numbers if <code>true</code>, generated string will include numeric characters
     * @return the random string
     */
    public static String random(int count, int start, int end, boolean letters, boolean numbers) {
        return random(count, start, end, letters, numbers, null, RANDOM);
    }

    /**
     * <p>
     * Creates a random string based on a variety of options, using default source of randomness.
     * </p>
     *
     * <p>
     * This method has exactly the same semantics as {@link #random(int,int,int,boolean,boolean,char[],Random)}, but
     * instead of using an externally supplied source of randomness, it uses the internal static {@link Random}
     * instance.
     * </p>
     *
     * @param count the length of random string to create
     * @param start the position in set of chars to start at
     * @param end the position in set of chars to end before
     * @param letters only allow letters?
     * @param numbers only allow numbers?
     * @param chars the set of chars to choose randoms from. If <code>null</code>, then it will use the set of all
     *        chars.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not <code>(end - start) + 1</code> characters in the set
     *         array.
     */
    public static String random(int count, int start, int end, boolean letters, boolean numbers, char[] chars) {
        return random(count, start, end, letters, numbers, chars, RANDOM);
    }

    /**
     * <p>
     * Creates a random string based on a variety of options, using supplied source of randomness.
     * </p>
     *
     * <p>
     * If start and end are both <code>0</code>, start and end are set to <code>' '</code> and <code>'z'</code>, the
     * ASCII printable characters, will be used, unless letters and numbers are both <code>false</code>, in which case,
     * start and end are set to <code>0</code> and <code>Integer.MAX_VALUE</code>.
     *
     * <p>
     * If set is not <code>null</code>, characters between start and end are chosen.
     * </p>
     *
     * <p>
     * This method accepts a user-supplied {@link Random} instance to use as a source of randomness. By seeding a single
     * {@link Random} instance with a fixed seed and using it for each call, the same random sequence of strings can be
     * generated repeatedly and predictably.
     * </p>
     *
     * @param count the length of random string to create
     * @param start the position in set of chars to start at
     * @param end the position in set of chars to end before
     * @param letters only allow letters?
     * @param numbers only allow numbers?
     * @param chars the set of chars to choose randoms from. If <code>null</code>, then it will use the set of all
     *        chars.
     * @param random a source of randomness.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not <code>(end - start) + 1</code> characters in the set
     *         array.
     * @throws IllegalArgumentException if <code>count</code> &lt; 0.
     * @since 2.0
     */
    public static String random(int count, int start, int end, boolean letters, boolean numbers, char[] chars,
            Random random) {
        if (count == 0) {
            return "";
        } else if (count < 0) {
            throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
        }
        if ((start == 0) && (end == 0)) {
            end = 'z' + 1;
            start = ' ';
            if (!letters && !numbers) {
                start = 0;
                end = Integer.MAX_VALUE;
            }
        }

        char[] buffer = new char[count];
        int gap = end - start;

        while (count-- != 0) {
            char ch;
            if (chars == null) {
                ch = (char) (random.nextInt(gap) + start);
            } else {
                ch = chars[random.nextInt(gap) + start];
            }
            if ((letters && Character.isLetter(ch)) || (numbers && Character.isDigit(ch)) || (!letters && !numbers)) {
                if (ch >= 56320 && ch <= 57343) {
                    if (count == 0) {
                        count++;
                    } else {
                        // low surrogate, insert high surrogate after putting it in
                        buffer[count] = ch;
                        count--;
                        buffer[count] = (char) (55296 + random.nextInt(128));
                    }
                } else if (ch >= 55296 && ch <= 56191) {
                    if (count == 0) {
                        count++;
                    } else {
                        // high surrogate, insert low surrogate before putting it in
                        buffer[count] = (char) (56320 + random.nextInt(128));
                        count--;
                        buffer[count] = ch;
                    }
                } else if (ch >= 56192 && ch <= 56319) {
                    // private high surrogate, no effing clue, so skip it
                    count++;
                } else {
                    buffer[count] = ch;
                }
            } else {
                count++;
            }
        }
        return new String(buffer);
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of characters specified.
     * </p>
     *
     * @param count the length of random string to create
     * @param chars the String containing the set of characters to use, may be null
     * @return the random string
     * @throws IllegalArgumentException if <code>count</code> &lt; 0.
     */
    public static String random(int count, String chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, chars.toCharArray());
    }

    /**
     * <p>
     * Creates a random string whose length is the number of characters specified.
     * </p>
     *
     * <p>
     * Characters will be chosen from the set of characters specified.
     * </p>
     *
     * @param count the length of random string to create
     * @param chars the character array containing the set of characters to use, may be null
     * @return the random string
     * @throws IllegalArgumentException if <code>count</code> &lt; 0.
     */
    public static String random(int count, char[] chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, 0, chars.length, false, false, chars, RANDOM);
    }

}
